Refractance window drying of food and biological materials

Heating water transmits heat energy within itself by conduction, convection, and radiation. Among them, radiation is the most rapid process. In RW dryer, the circulating water temperature is maintained between 95 and 98°C. During drying, the hot Refractance Window Dryer water surface is covered by a Mylar film which blocks the evaporation of water and its heat loss. Hence, the product temperature remains at 60-72°C. At this reduced temperature, the pharmaceutical and bioactive products can be dried efficiently.
Early understandings heat transfer mechanism inRW drying suggested that the moist material on a thin plastic sheet over hot water, creates a “window” for infrared radiation andas the material dries, the “window” gradually cuts off the radiation. Blueberries, being small fruits that contain heat sensitive compounds and distinct pigments that are likely to be lost or discolored during drying, will be used in the project. This research will not only increase competitiveness of a small business, but also introduces a relatively low cost drying method that has potential to maintain food product quality to satisfy the needs of increasingly health conscious consumers. It is expected that the outcome of phase I study will guide dryer design improvements in the next phase that will positively influence the retention of quality in  other types of dried food products, including protein, starch, and vegetable.

Basically, these are gas-solid contact operations working on gradients in water vapour pressures. Refractance Window is a relatively new drying technique for producing dried powders, slices or leathers from fruits and vegetables. In the present study, the effect of temperature (70, 80 and 90 °C) and thickness of puree on drying characteristics, mass transfer and quality attributes of RW dried banana puree were investigated. Results showed that drying at 90 °C reduced drying time (~61–64%) and energy consumption (~30–44%), as compared to drying at a lower temperature (70 °C) for both the thickness.
Mathematical modeling was performed from drying kinetics data using the Lewis, Henderson-Pabis, Page, and Logarithmic models. Activation Energy and Diffusivity were also determined. The model with the best fit was the logarithmic one, with a correlation coefficient greater than 0.99. The obtained activation energies were 22.81 kJ mol−1 for Refractance window and 31.44 kJ mol−1 using conventional hot air drying while a diffusivity of 2.9 ∗10−8 m2 s−1 for RW and 1.3∗10−8 m2 s−1 for CO were found as well.
•RWD patents are based on designing process or drying systems for process economy. Khir R., Pan Z., Salim A., Hartsough B.R., Mohamed  S. Moisture diffusivity of rough rice underinfrared radiation drying. Akinola A., Ayo D., Ezeorah S. Temperature dependence of the effective moisture diffusivity of yam slices dried using a Refractance WindowTM dryer. Cabrera Ordoñez Y., Estrada E., Cortés M. The influence of drying on the physiological quality of cape gooseberry (Physalis peruviana L.) fruits added with active components. Kaymak-Ertekin F., Gedik A. Kinetic modelling of quality deterioration in onions during drying and storage.

According to MCD, besides its gentle drying characteristic, Washington State University research has calculated that  the Refractance Window dryer is 99% efficient in its heat transfer. Its automated operation reduces labor costs and the transparent belt design allows quick cleanup and minimizes maintenance. RW-dried strawberries demonstrated color values close to that measured in freeze-dried samples.
The Total Phenolic Content of the refractance window dried sample obtained at 90 °C was found maximum to be 2710 ± 2.75 mg GAE/100 g. The IC50 value of Refractance window dried walnut kernel was found lowest (4.12 ± 0.45 µg/mL) at 50 °C. The Lipoxygenase activity of all samples was significantly lower in the case of Refractance window drying. Based on the ΔE value and water activity of the refractance window dried sample showed better results at 70 °C. At 50 °C and 60 °C the parameters like fat content, Antioxidant activity lipoxygenase activity, and IC50 show better condition. Results suggest that RW technique has tremendous potential for drying walnut kernels which could be scaled up at the industrial level for commercial purposes with its added advantages such as low cost, shorter drying time, easy handling, and maintenance of the equipment.

Later that day, I went to an ocean beach to swim and began to think of a way to preserve these foods. After exploring several different ideas, I concluded that the most cost effective way to preserve food was to dry it. “Work done to date has demonstrated that RW dried strawberry retains more Vitamin C than freeze-drying and similar levels of Vitamin A,”​ she said. Refractance Window Drying or Drying Technology is considered as the novel fourth-generation drying technique that has been gaining much attention nowadays, owing to its numerous benefits. At MegaFood, it’s the same dilemna.
Two optimisation systems were formulated; one for a nanoemulsion made from formulation A and the other for a nanoemulsion made with formulation B , both having  minimum moisture and water activity after RW drying. The water activity of the flakes was measured using an AquaLab Series 4 aw meter (Decagon Devices, Inc., Pullman, WA) after the samples were stabilized at 25 °C for 30 min31. The measurements were performed in triplicate.
Effects of infrared-assisted Refractance Window™ drying on  the drying kinetics, microstructure, and color of physalis fruit purée. The aim of this study was to investigate the moisture and oil uptake capacities of gluten-free chips by pre-drying at different temperatures and times before deep frying. In addition, the determination of some physicochemical contents and sensory propert... & Topuz, A. Effects of different drying methods on the physicochemical properties of pomegranate leather . & Young, B. R. A review towards hyperspectral imaging for real-time quality control of food products with an illustrative case study of milk powder production. At the end of the drying process, the material is passed over the belt cooled with cold water from below, and separated from the belt by the scraper device.